JP2015187430A - internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately treat unburned fuel components left in the combustion chamber of a cylinder when a combustion failure in an air-fuel mixture occurs.SOLUTION: An internal combustion engine that can implement active ignition for generating plasmas in a combustion chamber by the interaction between spark discharge generated between a center electrode and a ground electrode of an ignition plug 12 and an electric field emitted into the combustion chamber via an antenna facing the interior of the combustion chamber and thereby igniting a fuel, re-implements the active ignition upon lowering a voltage for the spark discharge to be applied to the electrodes of the ignition plug 12 from the last applied voltage, weakening an electric field to be emitted into the combustion chamber from the last emitted electric field, or shortening time for emitting the electric field into the combustion chamber from the time for emitting the last emitted electric field.

Description

  The present invention relates to an internal combustion engine mounted on a vehicle or the like.

  In an ignition device mounted on a general spark ignition type internal combustion engine, a high voltage generated in the ignition coil when the igniter extinguishes is applied to the center electrode of the ignition plug, so that the center electrode of the ignition plug is grounded. A spark discharge is caused between the electrodes and ignited.

  Recently, in order to ensure that the air-fuel mixture in the combustion chamber of the cylinder is ignited and a stable flame can be obtained, the high frequency output from the high frequency oscillator or the microwave output from the magnetron is radiated into the combustion chamber. An “active ignition” method has been attempted (see, for example, the following patent document). According to the active ignition method, a high-frequency electric field or a microwave electric field is formed in the space between the center electrode and the ground electrode, and the plasma generated in this electric field grows to form a large flame nucleus that starts flame propagation combustion. Can be generated.

JP 2011-0664162 A

  The active ignition method is a promising technique for improving the certainty of ignition of the air-fuel mixture, but does not prevent misfire. If misfire occurs, unburned fuel components are discharged from the cylinders into the exhaust passage, leading to worsening of emissions. In addition, there is a concern that unburned fuel causes an oxidation reaction in the three-way catalyst for exhaust purification, causing the temperature of the catalyst to rise abnormally.

  Further, in an in-cylinder direct injection internal combustion engine that directly injects fuel into the combustion chamber of the cylinder, the fuel injected from the injector may adhere to the electrode portion of the spark plug. This adhered fuel becomes a factor that inhibits spark discharge between the center electrode of the spark plug and the ground electrode, and increases the risk of causing misfire. Once misfiring occurs, the possibility of repeated misfiring increases due to the fuel adhering to the electrode even after the next cycle.

  An object of the present invention is to suitably treat an unburned fuel component remaining in a combustion chamber of a cylinder when an air-fuel mixture combustion failure occurs.

  In order to solve the above-described problems, in the present invention, the spark discharge generated between the center electrode and the ground electrode of the spark plug interacts with the electric field radiated into the combustion chamber via the antenna facing the combustion chamber. It is possible to perform active ignition that generates plasma in the combustion chamber and ignites the fuel, and the combustion failure in the combustion chamber of the cylinder (the injected fuel does not burn sufficiently and unburned fuel components are in the combustion chamber) When it is sensed that the remaining state (combustion instability or misfire) has occurred, when the pressure in the combustion chamber of the cylinder is below a predetermined level, the spark discharge voltage to be applied to the electrode of the spark plug is immediately before that. When the electric field that is lower than the applied voltage, the electric field to be radiated in the combustion chamber is weaker than the electric field radiated immediately before, and / or the time of radiating the electric field in the combustion chamber is radiated immediately before And configure the internal combustion engine to re-execute the active ignition after having shorter than.

  According to the present invention, it is possible to suitably treat the unburned fuel component left in the combustion chamber of the cylinder when the combustion failure of the air-fuel mixture occurs.

The figure which shows schematic structure of the internal combustion engine of one Embodiment of this invention. The circuit diagram of the ignition system of the internal combustion engine of the embodiment. The figure explaining the structure of the electric field generator accompanying the ignition system of the internal combustion engine of the embodiment. The circuit diagram of the H bridge which is an element of the electric field generator. The timing diagram which shows transition of the ionic current at the time of normal combustion in the internal combustion engine of the embodiment. The figure which shows transition of the primary current which flows through the primary side coil of an ignition coil in the period from ignition of an igniter to spark ignition.

  An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an outline of an internal combustion engine for a vehicle in the present embodiment. The internal combustion engine in the present embodiment is a direct injection type four-stroke gasoline engine and includes a plurality of cylinders 1 (one of which is shown in FIG. 1). Each cylinder 1 is provided with an injector 11 for injecting fuel at a position facing the combustion chamber. A spark plug 12 is attached to the ceiling of the combustion chamber of each cylinder 1.

  FIG. 2 shows an electric circuit of the ignition system. The spark plug 12 receives spark voltage generated by the ignition coil 14 and causes spark discharge between the center electrode and the ground electrode. The ignition coil 14 is integrally incorporated in the coil case together with the igniter 13 having the semiconductor switching element 131.

  When the igniter 13 receives an ignition signal i from an ECU (Electronic Control Unit) 0, which is a control device for the internal combustion engine, first, the semiconductor switch 131 of the igniter 13 is ignited and a current flows to the primary side of the ignition coil 14, immediately thereafter. At this spark ignition timing, the semiconductor switch 131 extinguishes and this current is cut off. Then, a self-induction action occurs, and a high voltage is generated on the primary side. Since the primary side and the secondary side share the magnetic circuit and the magnetic flux, a higher induced voltage is generated on the secondary side. This high induction voltage is applied to the center electrode of the spark plug 12, and a spark discharge is generated between the center electrode and the ground electrode.

  The primary coil of the ignition coil 14 is connected to the in-vehicle power supply battery 17 via the semiconductor switch 131. When the semiconductor switch 131 is ignited and a DC voltage supplied from the battery 17 is applied to the primary side coil to start energization, the primary current flowing through the primary side (low voltage system) circuit including the primary side coil increases.

FIG. 6 illustrates the transition of the primary current after the start of energization of the primary side coil. In FIG. 6, the case where the current limiting function does not work is drawn with a broken line, and the case where the current limiting function works is drawn with a one-dot chain line (the solid line will be described later). Assuming that the primary side electric circuit including the battery 17 and the primary side coil is an RL series circuit, the primary current I (t) when the DC voltage E is applied at time t = 0 is
I (t) ≈ {1-e- ^{(R / L) t} } E / R
It becomes. That is, the primary current increases as a transient phenomenon, but the rate of increase gradually decreases. When a sufficiently long time elapses, the primary current saturates to E / R as shown by the broken line in FIG.

  The igniter 13 has a current limiting function that suppresses excessive primary current. This current limiting function is similar to that of off-the-shelf igniters that are popular today. Specifically, the control circuit 132 constantly measures the primary current in the form of the voltage across the resistor 133 via the detection resistor 133. The semiconductor switch 131 is ignited while the magnitude of the primary current (voltage across the resistor 133) is equal to or less than a specified value, while the semiconductor switch 131 is extinguished when the magnitude exceeds the specified value. As a result, the primary current is clipped to the specified value as indicated by the alternate long and short dash line in FIG.

The induced voltage applied to the center electrode of the spark plug 12 at the time of spark ignition becomes higher as the primary current flowing in the primary coil of the ignition coil 14 at the time t ₁ when the semiconductor switch 131 is extinguished is larger. Therefore, the longer the energization time to the primary coil, the higher the induced voltage applied to the center electrode of the spark plug 12. In addition, a large primary current means that the amount of electric power input to the ignition coil 14 is large, and the longer the energization time to the primary coil, the spark between the center electrode of the spark plug 12 and the ground electrode. The time during which discharge continues is also increased.

In short, it is possible to adjust the magnitude of the induced voltage applied to the center electrode of the spark plug 12 and the duration of the spark discharge by adjusting the time points t ₀ and t ₀ ′ when the semiconductor switch 131 is ignited. . In FIG. 6, a case where the energization time to the primary side coil is relatively short (energization starts at a later time t ₀ ) is drawn with a solid line, and the energization time to the primary side coil is relatively long (earlier time t _The energization is started from ₀ ').

  Incidentally, the igniter 13 also has a function of forcibly cutting off the energization to the primary side coil when detecting abnormal heat generation such that the temperature of the ignition coil 14 or the igniter 13 itself exceeds the upper limit value.

  In the internal combustion engine of the present embodiment, an electric field generator 6 for generating an electric field in the combustion chamber of the cylinder 1 is attached to the ignition system. The electric field generator 6 is intended to generate plasma in the combustion chamber. Specific examples of the electric field generator 6 include an AC voltage generation circuit that outputs a high-frequency AC voltage, a pulsating voltage generation circuit that outputs a high-frequency pulsating voltage, and the like.

  As shown in FIGS. 3 and 4, the electric field generator 6 that generates a high frequency includes a circuit that uses a vehicle-mounted battery as a power source and converts low-voltage direct current into high-voltage alternating current. Specifically, a DC-DC converter 61 that boosts a DC voltage of about 12 V provided by the battery to 100 V to 500 V, and an H-bridge circuit 62 that is a high-frequency generation circuit that converts the DC output from the DC-DC converter 61 into AC. And a step-up transformer 63 that boosts the alternating-current high-frequency output from the H-bridge circuit 62 to a higher voltage.

  The DC-DC converter 61 can change the magnitude of the direct-current drive voltage applied to the H bridge circuit 62 in response to the command 1 from the ECU 0, and consequently the amplitude of the high-frequency voltage downstream of the step-up transformer 63. Can be changed. The high-frequency voltage downstream of the step-up transformer 63 preferably has a frequency of about 200 kHz to 3000 kHz and an amplitude of about 3 kVp-p to 10 kVp-p.

  A first diode 64 and a second diode 65 are interposed at the output end of the electric field generator 6. The first diode 64 has a cathode connected to the signal line of the secondary winding of the step-up transformer 63 and an anode connected to the mixer 7, which is a node with the ignition coil 14. The second diode 65 has an anode connected to the ground line of the secondary winding of the step-up transformer 63 and a cathode grounded. The first diode 64 and the second diode 65 rectify the high frequency of alternating current by half-wave rectification downstream of the step-up transformer 63 and pulsate the negative high-voltage pulse current flowing from the secondary side of the ignition coil 14 at the ignition timing. Play a role of blocking.

  Incidentally, when a pulsating voltage generation circuit is employed as the electric field generator 6, the pulsating voltage generation circuit may be any circuit that generates a DC voltage whose voltage periodically changes, and its waveform may be arbitrary. . The pulsating voltage mentioned here includes a pulse voltage that varies from a reference voltage (which may be 0 V) to a constant voltage at a constant period, a voltage obtained by adding a DC bias to an AC voltage, and the like.

  The high frequency voltage generated by the electric field generator 6 is applied to the center electrode of the spark plug 12. That is, the center electrode of the spark plug 12 facing the combustion chamber of the cylinder 1 is an antenna that radiates an electric field. Thereby, a high frequency electric field is formed in the space between the center electrode of the spark plug 12 and the ground electrode in the combustion chamber. Then, a plasma is generated by performing a spark discharge in a high-frequency electric field, and this plasma generates a large radical plasma flame nucleus that starts flame propagation combustion.

  In the above, the flow of electrons due to the spark discharge and the ions and radicals generated by the spark discharge are vibrated and meandered by the influence of the electric field, resulting in a long path length and a dramatic increase in the number of collisions with surrounding water and nitrogen molecules. This is due to the increase. Water molecules and nitrogen molecules that have been struck by ions and radicals become OH radicals and N radicals, and the surrounding gas that has been struck by ions and radicals is also ionized, that is, a plasma state. In addition, the region of ignition of the air-fuel mixture increases and the flame kernel also increases. As a result, the two-dimensional ignition by only the spark discharge is amplified to the three-dimensional ignition, and the combustion rapidly propagates into the combustion chamber and expands at a high combustion speed.

  In the case of performing active ignition, the timing at which a high frequency is applied to the center electrode of the spark plug 12 is usually almost simultaneously with the start of spark discharge, immediately before the start of spark discharge, or immediately after the start of spark discharge.

  Of course, the internal combustion engine of the present embodiment can also ignite the air-fuel mixture by conventional spark ignition that is not active ignition, that is, spark discharge that does not involve emission of a high-frequency electric field from the center electrode of the spark plug 12. In situations where it is easy to ignite and burn stably (it is unlikely to cause a combustion failure), it is conceivable to perform conventional spark ignition to suppress power consumption.

  In the present embodiment, the ECU 0 can detect an ionic current generated in the combustion chamber of the cylinder 1 during the combustion of the air-fuel mixture, and determine the combustion state with reference to the ionic current signal h.

  As shown in FIG. 2, in this embodiment, a circuit for detecting an ionic current is added to the electric circuit of the ignition system. This detection circuit includes a bias power supply unit 15 for effectively detecting an ionic current and an amplification unit 16 that amplifies and outputs a detection voltage corresponding to the amount of the ionic current. The bias power supply unit 15 includes a capacitor 151 that stores a bias voltage, a Zener diode 152 for increasing the voltage of the capacitor 151 to a predetermined voltage, current blocking diodes 153 and 154, and a load that outputs a voltage corresponding to the ion current. A resistor 155. The amplifying unit 16 includes a voltage amplifier 161 typified by an operational amplifier.

  The capacitor 151 is charged during arc discharge between the center electrode and the ground electrode of the spark plug 12, and then an ion current flows through the load resistor 155 by the bias voltage charged in the capacitor 151. The voltage between both ends of the resistor 155 generated by the flow of the ionic current is amplified by the amplifying unit 16 and received by the ECU 0 as the ionic current signal h.

  FIG. 5 illustrates respective transitions of the ionic current (indicated by a solid line in the figure) and the combustion pressure in the cylinder 1 (in-cylinder pressure; indicated by a broken line in the figure) in normal combustion. In the case of normal combustion, the ionic current decreases by a chemical reaction before the compression top dead center after the end of spark ignition, and then increases again by thermal dissociation. At almost the same time as the in-cylinder pressure reaches its peak, the ion current also becomes maximum.

  Note that the ionic current cannot be detected during discharge for ignition. Further, what is shown in FIG. 5 is a waveform of the ion current signal h when the air-fuel mixture is burned by the conventional spark ignition. When performing active ignition in which a high-frequency electric field is radiated from the center electrode of the spark plug 12, ion current cannot be detected even during the emission of the high-frequency electric field.

  An intake passage 3 for supplying intake air to the cylinder 1 of the internal combustion engine takes in air from the outside and guides it to the intake port of each cylinder 1. On the intake passage 3, an air cleaner 31, an electronic throttle valve 32, a surge tank 33, and an intake manifold 34 are arranged in this order from the upstream.

  The exhaust passage 4 for exhausting the exhaust from the cylinder 1 guides the exhaust generated as a result of burning the fuel in the cylinder 1 from the exhaust port of each cylinder 1 to the outside. An exhaust manifold 42 and an exhaust purification three-way catalyst 41 are disposed on the exhaust passage 4.

  The external EGR (Exhaust Gas Recirculation) device 2 realizes a so-called high pressure loop EGR, and an EGR passage 21 communicating the upstream side of the catalyst 41 in the exhaust passage 4 and the downstream side of the throttle valve 32 in the intake passage 3. The EGR cooler 22 provided on the EGR passage 21 and the EGR valve 23 that opens and closes the EGR passage 21 and controls the flow rate of the EGR gas flowing through the EGR passage 21 are used as elements. The inlet of the EGR passage 21 is connected to the exhaust manifold 42 in the exhaust passage 4 or a predetermined location downstream thereof. The outlet of the EGR passage 21 is connected to a predetermined location downstream of the throttle valve 32 in the intake passage 3, specifically to a surge tank 33.

  The ECU 0 that controls operation of the internal combustion engine is a microcomputer system having a processor, a memory, an input interface, an output interface, and the like.

  The input interface includes a vehicle speed signal a output from a vehicle speed sensor that detects the actual vehicle speed of the vehicle, a crank angle signal b output from an engine rotation sensor that detects the rotation angle and engine speed of the crankshaft, and depression of an accelerator pedal. An accelerator opening signal c output from a sensor that detects the amount or the opening of the throttle valve 32 as an accelerator opening (so-called required load), and a brake pedaling amount signal d output from a sensor that detects the amount of depression of the brake pedal The intake air temperature / intake pressure signal e output from the temperature / pressure sensor for detecting the intake air temperature and the intake pressure in the intake passage 3 (particularly the surge tank 33), and the water temperature sensor for detecting the cooling water temperature of the internal combustion engine are output. Output from the cam angle sensor at a plurality of cam angles of the cooling water temperature signal f and the intake camshaft or exhaust camshaft. A cam angle signal g, the ion current signal h or the like to be output from the circuit for detecting an ion current caused by the combustion of the mixture in the combustion chamber are inputted.

  From the output interface, the ignition signal i for the igniter 13 of the spark plug 12, the fuel injection signal j for the injector 11, the opening operation signal k for the throttle valve 32, and the DC for the DC-DC converter 61. A voltage command signal l for commanding the magnitude of the drive voltage output from the DC converter 61, an opening operation signal m, etc. are output to the EGR valve 23.

  The processor of the ECU 0 interprets and executes a program stored in the memory in advance, calculates operation parameters, and controls the operation of the internal combustion engine. The ECU 0 acquires various information a, b, c, d, e, f, g, and h necessary for operation control of the internal combustion engine via the input interface, knows the engine speed, and is filled in the cylinder 1. Estimate the intake volume. Based on the engine speed, intake air amount, etc., the required fuel injection amount, fuel injection timing (including the number of fuel injections per combustion), fuel injection pressure, ignition timing, and high-frequency electric field applied to the combustion chamber Various operating parameters such as whether or not to perform, the strength of the electric field, and the required EGR rate (or EGR amount) are determined. The ECU 0 applies various control signals i, j, k, l and m corresponding to the operation parameters via the output interface.

  Then, the ECU 0 in the present embodiment refers to the ion current signal h and determines whether or not a combustion failure has occurred in the combustion chamber of the cylinder 1. When a combustion failure is detected, active ignition is executed to oxidize or burn the unburned fuel component remaining in the combustion chamber of the cylinder 1.

  As shown in FIG. 5, the ECU 0 determines the length of the period T during which the magnitude of the ion current signal h detected after igniting the air-fuel mixture charged in the combustion chamber of the cylinder 1 exceeds the threshold (crank Count the angle (° CA) or seconds). If the length of the counted period T is equal to or greater than the determination value, it is determined that the air-fuel mixture has burned normally during the expansion stroke of the cylinder 1. On the contrary, if the length of the period T falls below the determination value, it is determined that the combustion of the air-fuel mixture in the expansion stroke of the cylinder 1 is poor, that is, combustion instability or misfire has occurred.

  The ECU 0 that determines that the combustion failure of the air-fuel mixture has occurred performs active ignition (application of a high-frequency electric field and spark discharge) in the cylinder 1 as soon as possible after the detection of the combustion failure. This active ignition is preferably performed during the same cycle as the cycle in which the combustion failure occurs (the series of intake-compression-expansion-exhaust is one cycle), and in particular, the same as the expansion stroke in which the fuel failure has occurred. It is preferable to carry out in the middle or later stage of the expansion stroke.

  Therefore, if the in-cylinder pressure in the expansion stroke of the cylinder 1 in which the combustion failure has occurred is equal to or less than a predetermined value, the active ignition executed after the detection of the combustion failure is performed immediately before the ignition (for the original ignition combustion). Ignition, which may be active ignition or conventional spark ignition), lower the induction voltage for spark discharge, weaken the high-frequency electric field radiated into the combustion chamber, The time for radiating the high-frequency electric field is further shortened, or a plurality or all of these are simultaneously implemented.

  In other words, the amount of power supplied to the cylinder 1 in the active ignition is made as small as possible (if the ignition executed immediately before is active ignition, it is made smaller than the amount of power at the time of active ignition that caused the combustion failure. The unburned fuel component remaining in the combustion chamber or adhering to the electrode portion of the spark plug 12 is oxidized or burned. In a situation where the in-cylinder pressure is relatively low, that is, the atmosphere density in the combustion chamber is relatively low, it is easy to generate plasma by spark discharge and electric field radiation. It is allowed to curb consumption.

  When the ECU 0 detects a combustion failure in a low load region where the accelerator opening is equal to or less than a predetermined value, or the intake amount (or fuel injection amount proportional to this) filled in the cylinder 1 is equal to or less than a predetermined value, the combustion failure is detected. It is assumed that the in-cylinder pressure of the cylinder 1 that has caused the engine is not more than a predetermined value, and active ignition is performed for processing unburned fuel with a small amount of supplied power. Alternatively, if a pressure sensor for detecting the in-cylinder pressure is mounted on the cylinder 1, unburned fuel in which the amount of supplied power is reduced when the measured value of the in-cylinder pressure of the cylinder 1 that senses the combustion failure is equal to or less than a predetermined value. Perform active ignition for processing.

  Even if the pressure sensor for detecting the in-cylinder pressure is not mounted on the cylinder 1, the in-cylinder pressure during the expansion stroke when the air-fuel mixture filled in the cylinder 1 is assumed not to burn can be predicted. For example, the engine speed, the intake pressure and the intake air temperature in the surge tank 33, the opening / closing timing of the intake valve (when the internal combustion engine is equipped with a VVT (Variable Valve Timing) mechanism), etc. are predicted in advance. Map data or a function formula that defines the relationship with the in-cylinder pressure during the expansion stroke is stored. The ECU 0 searches the map using the engine speed in the intake stroke of the cylinder 1, the intake pressure and intake temperature in the surge tank 33, the intake valve timing, etc. as keys, or substitutes these into the function formula, The predicted value of the in-cylinder pressure during the expansion stroke when it is assumed that combustion does not occur is obtained. Then, when the predicted value is equal to or less than a predetermined value and a combustion failure is detected, active ignition for processing unburned fuel with a small amount of supplied power is executed. In addition, it can be considered that instead of the predicted value of the in-cylinder pressure, the above-described map describes whether or not active ignition can be performed with a small amount of supplied power.

  On the other hand, if the in-cylinder pressure in the expansion stroke of the cylinder 1 in which the combustion failure has occurred is not less than a predetermined value, the spark discharge induced voltage is lowered or radiated into the combustion chamber in the active ignition executed after the detection of the combustion failure. The unburned fuel component remaining in the combustion chamber or adhering to the electrode portion of the spark plug 12 is surely prevented without further weakening the high-frequency electric field to be generated or shortening the time for radiating the high-frequency electric field into the combustion chamber. Oxidize or burn. On the contrary, in the active ignition after the detection of the combustion failure, the induction voltage for spark discharge is increased or the high frequency radiated into the combustion chamber as compared with the ignition performed immediately before (ignition for original ignition combustion). It is also conceivable to increase the electric field, to extend the time for radiating the high-frequency electric field in the combustion chamber, or to implement a plurality or all of them simultaneously.

  In the present embodiment, the spark discharge generated between the center electrode of the spark plug 12 and the ground electrode interacts with the electric field radiated into the combustion chamber via the antenna facing the combustion chamber (center electrode of the spark plug 12). In this case, active ignition for generating plasma in the combustion chamber and igniting the fuel can be executed, and when it is detected that a combustion failure has occurred in the combustion chamber of the cylinder 1, the pressure in the combustion chamber of the cylinder 1 is A spark discharge voltage to be applied to the electrode of the spark plug 12 when lower than a predetermined value is lower than the voltage applied immediately before it, and the electric field to be radiated into the combustion chamber is weaker than the electric field radiated immediately before; And / or the time of radiating the electric field in the combustion chamber is made shorter than the radiating time of the electric field radiated immediately before the active ignition is re-executed, so that the unburned fuel remaining in the combustion chamber You configure the internal combustion engine to process the minute.

  According to the present embodiment, since unburned fuel components can be oxidized or burned in a timely manner, emission deterioration can be suppressed, and unburned fuel is oxidized in the catalyst 41 to cause the catalyst 41 to melt. Can also be avoided.

  In addition, in a direct injection type internal combustion engine, unburned fuel can be prevented from becoming liquid and adhering to the electrode portion of the spark plug 12, and even if unburned fuel adheres, it can be removed in a timely manner. In addition, the certainty of ignition of the air-fuel mixture in the cycle after the next cycle in which the combustion failure has occurred increases, and unstable combustion or misfire does not occur repeatedly.

  In addition, since unburned fuel can be burned out and converted to engine torque, the required load can be satisfied and drivability can be improved, which can contribute to improved fuel efficiency.

  During normal operation except during high EGR rate operation where the air-fuel mixture combustion stability is low or at low temperatures, etc., ignition is performed only by spark discharge, and active ignition is performed only when a defective combustion is detected. A mode in which the fuel component of the fuel is treated can also be taken. Alternatively, active ignition is performed by emitting a high-frequency electric field with the minimum intensity in normal times, and when a poor combustion is detected, a weaker high-frequency electric field is emitted again to perform active ignition to remove unburned fuel components. It can also take the form of processing. Then, power consumption due to electric field radiation into the combustion chamber can be suppressed.

  The present invention is not limited to the embodiment described in detail above. For example, the electric field generator 6 for applying an electric field to the combustion chamber of the cylinder 1 is not limited to an AC voltage generating circuit that applies a high-frequency AC voltage or a pulsating voltage generator circuit that applies a high-frequency pulsating voltage. A magnetron or the like that outputs a microwave may be employed as the electric field generator 6, and active ignition may be performed by applying a microwave electric field into the combustion chamber of the cylinder 1.

  In the above-described embodiment, the center electrode of the spark plug 12 is an antenna for electric field radiation. However, an antenna separate from the spark plug 12 is provided in the cylinder 1, and a high-frequency electric field or micro wave is provided in the combustion chamber of the cylinder 1 through this antenna. A wave electric field may be emitted.

  The method for detecting the combustion failure of the air-fuel mixture in the combustion chamber of the cylinder 1 is not limited to the method of referring to the ion current signal h as in the above embodiment. As already described, there is a correlation between the transition of the ion current signal h and the transition of the in-cylinder pressure (combustion chamber pressure of the cylinder 1) or the in-cylinder temperature (combustion chamber temperature). When a pressure sensor for detecting the in-cylinder pressure or a temperature sensor for detecting the in-cylinder temperature is mounted on the cylinder 1, the combustion of the air-fuel mixture is performed based on the in-cylinder pressure or the in-cylinder temperature measured via the sensor. It is possible to determine whether it is normal or defective. Typically, the length of the period in which the in-cylinder pressure or the in-cylinder temperature exceeds the threshold value is compared with a determination value, and if the length of the period falls below the determination value, combustion failure in the combustion chamber of the cylinder 1 is detected. It is determined that it has occurred.

  Another example of the method for detecting poor combustion is one that refers to the rotational fluctuation of the internal combustion engine. Specifically, the time required for the crankshaft, which is the output shaft of the internal combustion engine, to rotate by a predetermined angle (for example, 30 ° CA) is repeatedly measured, and the required time previously measured from the required time measured this time. By subtracting the time, an index value of the amount of change in the required time, that is, the amount of decrease in the rotational speed for each predetermined angle is obtained. Then, the index value is compared with a determination value. If the index value exceeds the determination value, it is determined that a combustion failure has occurred in the combustion chamber of the cylinder 1.

  The internal combustion engine to which the present invention is applied is not limited to a so-called gasoline direct injection engine. Naturally, it is also conceivable to apply the present invention to a diesel engine, a HCCI (homogeneous-charge compression ignition) engine, or the like.

  Furthermore, the present invention can also be applied to a port injection type internal combustion engine that injects fuel into an intake port.

  Other specific configurations of each part can be variously modified without departing from the spirit of the present invention.

  The present invention can be used as an internal combustion engine mounted on a vehicle or the like.

0 ... Control unit (ECU)
DESCRIPTION OF SYMBOLS 1 ... Cylinder 11 ... Injector 12 ... Spark plug, antenna 13 ... Igniter 14 ... Ignition coil 6 ... Electric field generator 7 ... Mixer

Claims (1)

Active to generate a plasma in the combustion chamber and ignite the fuel by interacting the spark discharge generated between the center electrode and the ground electrode of the spark plug and the electric field radiated into the combustion chamber via the antenna facing the combustion chamber Can be ignited,
When it is detected that a combustion failure has occurred in the combustion chamber of the cylinder, a spark discharge voltage to be applied to the electrode of the spark plug is applied immediately before the pressure in the combustion chamber of the cylinder is equal to or lower than a predetermined value. Active ignition after lowering the voltage, making the electric field to be radiated in the combustion chamber weaker than the electric field radiated immediately before, or radiating the electric field in the combustion chamber shorter than the radiating time of the electric field radiated immediately before Re-run the internal combustion engine.

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